**Change in Atomic Mass of C-12 Atom**

To calculate the percentage change in the atomic mass of a C-12 atom, we need to consider the changes in the masses of both the electron and the proton.

**1. Original Atomic Mass of C-12 Atom:**
The atomic mass of a C-12 atom is defined as 12 atomic mass units (u). This is because the carbon-12 isotope has six protons and six neutrons, both of which contribute to the mass of the atom.

**2. Increased Mass of Electron:**
Given that the mass of the electron is increased by 1837 times, we need to find the new mass of the electron. The mass of an electron is approximately 1/1837th of the mass of a proton. Therefore, the new mass of the electron can be calculated as follows:
New Mass of Electron = 1837 * Mass of Proton

**3. Decreased Mass of Proton:**
Given that the mass of the proton is decreased by 2 times, we need to find the new mass of the proton. The mass of a proton is approximately 1.0073 atomic mass units (u). Therefore, the new mass of the proton can be calculated as follows:
New Mass of Proton = Mass of Proton / 2

**4. Calculation of New Atomic Mass:**
To calculate the new atomic mass of the C-12 atom, we need to add the new masses of the electron and the proton to the original mass of the neutron (which remains unchanged). The neutron contributes to the atomic mass but is not affected by the given changes.
New Atomic Mass = Original Mass of Neutron + New Mass of Proton + New Mass of Electron

**5. Calculation of Percentage Change:**
Finally, to find the percentage change in the atomic mass of the C-12 atom, we can use the following formula:
Percentage Change = ((New Atomic Mass - Original Atomic Mass) / Original Atomic Mass) * 100

By substituting the calculated values into the formula, we can determine the percentage change in the atomic mass of the C-12 atom.

It is important to note that performing the calculations using the actual values will yield the precise percentage change.